A metal loaded catalyst in which various catalytic metal species are loaded on a catalyst carrier made of a metal oxide is used in an extremely wide range of fields, for example, not only dehydrogenation reaction in which hydrogenated aromatics such as methylcyclohexane, cyclohexane, and decalin are dehydrogenated into the corresponding aromatics and hydrogen but also manufacturing of chemical products and fuels by dehydrogenation reaction of various compounds, hydrogenation reaction which is a reverse reaction of the dehydrogenation reaction and reforming reaction; and environmental clean-up such as cleaning automobile exhaust gas, and the like.
Generally, such metal loaded catalysts are manufactured as follows: a porous catalyst carrier made of a metal oxide such as alumina or silica etc., is prepared; when platinum is loaded on the obtained porous catalyst carrier, the obtained porous catalyst carrier is impregnated with a solution of a catalyst metal compound, such as a chloroplatinic acid aqueous solution, a platinum ammonium chloride aqueous solution, and a solution of an organoplatinum compound such as platinum acetylacetonate; the resultant is dried to form a dried matter loading the catalyst metal compound; the dried matter is calcined, e.g., at 350 to 800° C. for 0.5 to 24 hours to form a calcined matter loading the catalyst metal compound; and, as required, the obtained calcined matter loading the catalyst metal compound is subjected to hydrogen reduction, e.g., at 250 to 800° C. for 0.5 to 24 hours.
However, the metal loaded catalyst manufactured by such a procedure has the following problems. For example, when a platinum-loaded alumina catalyst in which platinum, being one of typical active metal species as catalyst metal, is loaded on an alumina carrier, being used most widely as a catalyst carrier, is taken as an example, it is known that since the adsorbability of a platinum compound to the alumina carrier is high, the platinum compound is adsorbed and fixed as it is to the outer shell part of the alumina carrier before the platinum compound is dispersed inside the alumina carrier, which forms a so-called egg shell-type metal loaded catalyst, as viewed in the cross section, the catalyst metal being loaded only on the outer shell part and no catalytic metal species being loaded inside the carrier (see 14th “Catalysis School Text” (2003), pages 35 to 44 and 15th “Catalysis School Text” (2004), pages 35 to 44, organized by Kanto Branch Commission, Catalysis Society of Japan).
In the case of the reaction in which the dispersion resistance is high inside a catalyst, the reaction occurs preferentially in the outer shell of the catalyst. Thus, the egg shell-type catalyst is advantageous in such a reaction. However, when a certain amount of active metal is to be loaded only on the outer shell of the catalyst particles, the density of the active metal particles increase, which presumably leads to possibilities that the active metal particles can not be sufficiently dispersed, catalyst deactivation due to sintering or coking is likely to occur, etc. Therefore, in a reaction which is not influenced by the dispersion resistance, it is presumably advantageous to design a catalyst in such a manner as to reduce the influences by fully utilizing the surface area of a carrier.
However, it is not easy that the active metal such as platinum is uniformly dispersed as far as the inside of catalyst carrier particles, and a method using a competitive adsorption agent having high adsorbability to a carrier has been used heretofore (Catalyst Design, volume 5, pages 134 to 141, Catalyst Lecture edited by Catalysis Society of Japan). However, also in the method, it is relatively difficult to prepare a catalyst in which the active metal is uniformly dispersed thoroughly, and there is a possibility that the concentration gradient of loaded metal appears toward the center of the catalyst particles.    Non-patent Document 1: 14th “Catalysis School Text” (2003), pages 35 to 44, organized by Kanto Branch Commission, Catalysis Society of Japan    Non-patent Document 2: 15th “Catalysis School Text” (2004), pages 35 to 44, organized by Kanto Branch Commission, Catalysis Society of Japan    Non-patent Document 3: Catalyst Design, volume 5, pages 134 to 141, Catalyst Lecture edited by Catalysis Society of Japan